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Syntheses, Reactivity a n d Complexation Properties of nido-2,3.5-Tricarbahexaboranes* By double hydroboration of 1,3-dihydro-1,3-diborafulvenes 2 or 4,5-diisopropylidene-1,3-diborolanes 3 with (Et2BH)2 and subsequent loss of triethylborane derivatives 1 of 2,3,5-tricarbahexaborane are formed under mild conditions. The stability of the nido-carboranes 1 depends on the substituents in the basal positions. After deprotonation, the tricarbahexaboranate ion (1 -H)functions as a cyclopentadienyl analogue (C,H,)-, and its reaction with allylnickel bromide dimer gives the allylnickel complexes 8a, b. Reaction of octacarbonyl dicobalt with 1 b yields the dicarbonylcobalt complex lob. Treatment of l e with [(C,H,)Ni(CO)]2 results in the formation of the dinuclear carbonyl-bridged complex 12 e. Von den Vertretern der nido-Carborane rnit pentagonaler Basisflache sind vor allem Derivate des C2B9Hl3['I und des C2B4H8r21 zum Aufbau von closo-Metallacarboranen untersucht ord den[^-^]. In der Reihe der nido-Cluster C,B6 nHlo fehlten bislang Derivate von 2,3,5-Tricarbahexaboran (n = 3), wahrend Beispiele fur das 2,3,4-Isomer schon seit 1968 bekannt sind@'. Wir haben 1984 erstmals die Bildung von (2,3,5-Tricarbahexaboranyl)nickel-Komplexen aus der Bis(2,3-dihydro-1,3-diborol)nickel-Verbindung A be~bachtet~". Dabei entsteht durch Eliminierung von Wasserstoff aus A und Uberdachung des postulierten Bis(2,3-dihydro-1,3-di-boroly1)nickeLSandwichs (1 6 VE) rnit einer Methylborandiyl-Einheit [Me-B] der 18-VE-Komplex B. Des weiteren bilden sich durch Stapelreaktionen die Oligodecker-Komplexe C (n = 1 -8). In

peri‐Überbrückung bei Naphthalin durch ein Boratom bewirkt in dem Naphtho[l,8‐bc]boret 1 eine starke Abweichung der sp2‐Bindungswinkel an C1 und C8 vom Idealwert. Die daraus resultierende Ringspannung prägt die Chemie von 1: Bei der Umsetzung mit elektronenarmen Borverbindungen EX3 wird eine unerwartete Ringexpansion zu 2 (X = CI, Br, OEt) beobachtet.

Z. Naturforsch. 51 b, 1104Z. Naturforsch. 51 b, -1110Z. Naturforsch. 51 b, (1996; eingegangen am 22. Januar 1996The synthesis and structural properties of organo-bis-dialkylaminochlorboranes X( BNR2C1)2 X = R2NB(CHCH3)2, < 9-C6H4, 1-q-C6H4CH2, and 1.8-C10H6 are reported. The steric influ ence of the alkylamino group and the geometrical situation caused by a chain of sp2 or sp3 hybridized carbon atoms control the formation of intramolecular donor-acceptor bonds. In o ( C 6H4)(BNM e2C l)2 (5) only one amino-boron donor-acceptor bond is observed. The steric influence of the alkyl groups in R2NB(CHCH3BC1NR2)2 is discernible from the formation of two donor-acceptor bonds in 7a (R = Me), whereas 7b (R = /Pr) is a non-bridged species.The reaction of benzomagnesacyclobutene with chlorbis(dimethylamino)borane yields cyclic l-a (C 6H4C H 2)(BNM e2C l)2 (9). 1,8-Dilithionaphthalene reacts with C1B (NR2)

1994organo-boron compounds, nonmetal heterocycles organo-boron compounds, nonmetal heterocycles S 0047 -184Synthesis and Reactivity of a Naphtho(1,8-bc)boret.-Treatment of the naphthalene (I) with the boron compound (II) leads to the novel title compound (III). It reacts with BX3 to afford the products (IV) by a novel ring expansion. Coupling of (III) with BHEt2 and B2H6 gives the borones (VI) and (VII), respectively. -(HERGEL, A.; PRITZKOW, H.; SIEBERT, W.; Angew.